1. Field of the Invention
The present invention relates to water treatment, and more specifically, to a method and apparatus for purifying potable water for use in ice machines and beverage machines.
2. Description of Related Art
Commercial ice-making machines and beverage dispensing machines are susceptible to contamination by microorganisms such as bacteria, yeast, fungi, and mold. Once this equipment has become contaminated, these microorganisms may multiply and establish flourishing colonies that can form scale buildup in the lines, tubing, evaporator surfaces, drains and other parts of the machines. Furthermore, these microorganisms may present a serious health hazard to people ingesting the contaminated products dispensed from the ice or beverage machines.
The need to keep ice making and beverage dispensing equipment clean over time is well known. Therefore, in an ice-making machine for example, the ice-forming evaporator, fluid lines and ice storage areas of the ice machine must be periodically cleaned. While manual cleaning with detergents and sterilizing chemicals may be effective, cleaning schedules are not, as a practical matter, always adhered to nor may the job always be satisfactorily completed in terms of a thorough cleaning and rinsing of all the contacted surfaces. Thus, systems have been developed that include electronic controls to automatically execute a sanitizing cycle at set periods wherein cleaning agents are pumped through the system and then rinsed out. Of course, the automatic systems can fail as well, where, for example, the cleaning agent reservoir runs out of cleaner, or the apparatus simply breaks down or fails to operate properly.
The use of ozone (O3) as a sanitizing/oxidizing agent is well known, and especially well known is the use of O3 to kill microorganisms in water. In U.S. Pat. No. 6,153,105, Tadlock et al. placed a venturi in the circulating water line of an ice machine to use the circulating water as a motive fluid to entrain ozone from a corona discharge process into the circulating water. The corona discharge process generates ozone at a pressure below the potable water supply pressure to the ice machine, thereby requiring the use of a venturi. Thus, the circulating water, with the venturi, carries O3 over the ice making evaporator providing some bactericidal or bacteriostatic effect.
Ozone may also be produced by electrolysis, which advantageously can produce ozone at pressures greater than that of the circulating water line within the ice machine. Therefore, the ice machine would not require a venturi or other apparatus to inject the ozone into the water line. Electrolytic production of ozone occurs in an electrochemical cell by causing oxidation and reduction reactions that liberate or consume electrons. These reactions take place at electrode/solution interfaces, where the electrodes must be good electronic conductors. In operation, a cell is connected to an external load or to an external voltage source, and electrons transfer electric charge between the anode and the cathode through the external circuit. To complete the electric circuit through the cell, an additional mechanism must exist for internal charge transfer. One or more electrolytes provide internal charge transfer by ionic conduction. These same electrolytes must be poor electronic conductors to prevent internal short-circuiting of the cell.
Proton exchange membranes (PEM's) are one category of electrolytes that are particularly suitable for use in conjunction with the production of ozone in electrochemical cells. PEM's typically have a polymer matrix with functional groups attached that are capable of exchanging cations or anions. The polymer matrix generally consists of an organic polymer such as polystyrene, or other polytetrafluoroethylene (PTFE) analog. In general, the PEM material is an acid with a sulfonic acid group incorporated into the matrix.
Electrocatalysts are placed in intimate contact with the proton exchange membranes. Typical electrocatalysts for an ozone generator may be lead dioxide on the anode or ozone producing side of the cell and platinum black on the cathode side of the electrochemical cell. In many such cells, hydrogen gas is generated at the cathode as a byproduct of the electrolysis reaction that produces ozone at the anode.
Ultraviolet radiation can also kill microorganisms in water and other liquids. Conventionally, the ultraviolet light source is a mercury-vapor type lamp, producing the majority of the radiated energy at a wavelength of about 254 nanometers, a wavelength know to be effective in killing microorganisms in water. The lamp may be immersed in the water or liquid or the lamp may be placed adjacent to a liquid stream flowing in a transparent conduit or in a conduit having a transparent window through which the ultraviolet radiation may pass. In U.S. Pat. No. 6,153,105, Tadlock et al. uses ultraviolet radiation to treat the circulating water in an ice machine.
FIG. 1 is a schematic view of a conventional water circulation type icemaker. The icemaker is connected to a potable water supply 13 to provide makeup water to the reservoir 10. When the water level 16 in the reservoir 10 drops below a certain level, the level controller 11 sends a signal to the refill valve 12 to open and allow makeup water into the reservoir through a supply conduit 14. A circulation pump 15 circulates water through a circulation conduit 17 from the reservoir 10 to the ice tray/evaporator plates 18. The ice tray/evaporator plates 18 produce ice while excess water 19 overflows back into the reservoir 10.
While Tadlock et al. and others have made strides in treating water in ice machines and beverage machines, there are still problems that need to be solved. Because the water circulates throughout the system in the icemaker, microorganisms have the opportunity to grow and flourish because the water circulation gives the microorganisms the residence time required for them to multiply and establish colonies. Furthermore, additional microorganisms are introduced into the system whenever the makeup water fills the reservoir by batch. Accordingly, water treatment must occur when the batch is brought into the reservoir at a fairly high rate, making adequate treatment more difficult. Ozone treatment is made more difficult because the source of the ozone must be capable of varying the ozone production rate in proportion to the water refill rate up to an amount adequate to treat a large influx of water when the batch fill of the reservoir takes place.
What is needed is an apparatus that can treat ice making and beverage dispensing machines to keep them free of microorganism contamination. It would be an advantage if such an apparatus could provide disinfecting quantities of biocide on demand in response to a batch filling of the reservoir. It would be further advantageous if the apparatus could provide and distribute the biocide sufficiently to preclude microorganism growth throughout the system, including both the areas used to produce the ice or beverage and the areas used to dispense the ice or beverage.